Method for Producing Wood Fibre Pellets

ABSTRACT

A process for producing pellets or granules comprising fibres of a lignocellulousic material, for use as a feedstock in plastics manufacture, conveying in a dry or wet air stream and applying to the fibres a liquid formulation comprising one or more polymers, monomers, or oligomers, forming the fibres into a solid product, and breaking down the solid product to produce said pellets or granules. Typically the conduit conveys the fibres in a plant for manufacture of fibre board.

FIELD OF INVENTION

The invention relates to a process for producing pellets or granulescomprising fibres of a lignocellulosic material or natural fibres, foruse as a feedstock in plastics manufacture.

BACKGROUND

The combining of cellulose-based materials to plastics was originallydeveloped over 25 years ago by extrusion machinery manufacturer ICMA SanGiorgio⁽¹⁾ and used by G.O.R. Applicazioni Speciali SpA to make doorpanels for FIAT cars. The materials for this process were pre-mixed andcram-fed.

Specialist machines have recently been developed in the composite marketto produce window and door profiles, as well as decking boards, usinghardwood and softwood flour. Generally this equipment is based ontraditional plastics manufacturing technologies including extrusion andinjection moulding. The plastics used include polypropylene (PP),polyethylene (PE) and poly-vinyl-chloride (PVC) and the fillers usedinclude wood flour, flax, jute and other cellulose-based fibre fillers.The more cellulose-based material that is added to the plastic, oftenthe lower the price and, often, the higher the stiffness of thewood-plastic “raw” material. The composite products made from thesewood-plastics can generally be nailed, painted and otherwise treated aswood whilst potentially retaining many of the benefits of plastics inthe areas of fungal and corrosion resistance.

For some, addition of wood flour has drawbacks in that, comparedconventional inorganic fillers for plastics, it is low bulk density andoften needs significant pre-drying before or during compounding, whichcan result in low production rates and high costs. The powderyconsistency of such fillers not only results in a messy operation, andmay pose potential health risks to those manning the processing. Woodflour (and wood fibre) also tend to cause blocking in addition port orhoppers, bridging or agglomeration due to the material packing togetherand can be more difficult to convey and feed into an extruder comparedto conventional plastic fillers, the inlet of which is typically smallrelative to the low bulk density of these materials.

A number of commercial enterprises have recognised some of theseproblems and have developed, for sale, pre-pelletised wood flour forconvenient feeding into extruders⁽²⁾. Other have patented processes orconcepts around production of pellets containing wood flour andthermoplastic material for further processing such as extrusion⁽³⁾. Somehave compatibilisers or additives to give enhanced properties⁽⁴⁾, withmost still focused on wood flour.

Wood flour is a finely ground wood cellulose. When the particle size isabove 20 mesh or below 850 microns, the product generally is consideredto be wood flour. Mesh size is the measurement of number of openings ina screen per linear inch. The collected wood flour from various sources(sawdust, planar shavings, sanding dust and scraps) are hammer milled toform very fine powder, classified by the standard mesh size that it canpass through. Most wood-filled thermoplastic manufacturers specify flourin the 30-80 mesh range. Bulk density of wood flour is relatively highercompared to wood fibres. The moisture content of wood has a significanteffect on the processing and final composite product quality. Pre-dryingthe wood flour to less than 1% moisture content is usually desirable.Wood flour with less moisture content is less likely to burn duringcompounding with thermoplastics. The particle size for other naturalfibres/fillers such as pine needles, maple, oak, bamboo dust, jute andcoir may vary from 10-80 mesh. (From: Thermoplastic Composites—a NewBusiness Avenue, M Suresh Babu, Sangeeta Baksi, G. Srikant & SoumitraBiswas (www.tifac.org.in/news/acthermocomp.htm).

Commercial wood flour often comes in mesh sizes of 20 to 100, but mostthermoplastic applications are in the 30 or 40 mesh to 80 mesh range.Wood “fibre” is, strictly speaking, not the same as wood flour though,confusingly, the term “fibre” is used interchangeably for flours. Woodfibre, as opposed to wood flour, will typically be longer fibre-likerather than particle-like (flour) and may typically have average lengthsof >0.85 mm, and more usually >1 mm, and perhaps in the 2-3 mm range.Some powder (fines) may be present in the fibre products, but they areusually minor components and average lengths are thus greater in fibrerather than flour. In addition, often, fibre is more entangled orfluffy, of lower bulk density, and difficult to handle. The aspect ratio(length÷diameter) of, for example, wood fibres may be >10:1 and maytypically be, for example, of the order of 20:1, 25:1 or 40:1, 50:1,70:1 or more, while “flour” may generally have aspect ratios of 1:1 to4:1 or 5:1, and typically less than 8:1 or 10:1. Some wood flour ispulverized flour as fine as 200 mesh. There may be exceptions, but flouris generally a powdery product and fibre a longer fibrous-like material.Wood flour adds some stiffness to plastics but can reduce strengthand/or impact strength. However, the longer, higher aspect ratio, woodfibres contribute more to either or both stiffness and strength,compared to wood flour, while being lighter than many synthetic fibres.However, wood fibres are more difficult to blend and bind into theplastic-composites. The performance advantages of using wood fibresinstead of wood flour have been recognized⁽⁵⁾ but attempts to producespecial equipment to handle wood fibre to compound with a plastic havemet with limited success. Special fibre feeders or ‘stuffers’ or‘cratnmers’ are available but are often expensive and not reliable overa wide range of metering for end compositions since, for example, someapplications may require <10 wt % fibres while others may require morethan this and indeed >50 wt %. Mechanical properties including creepresistance have the potential to be improved by use of longer fibrescompared to flours or powder fillers.

The introduction of low bulk density natural or wood fibres intoextruders or injection moulders or other plastics processing machinery,in particular in a metered or measured way, which is important toachieve desired fibre volume fractions in compositions, has a number ofdifficulties. Thus, it is not staightforward, due to the inherent highvolume/low mass nature of such fibres, the lack of free flowingcharacteristics in such fibres, and the fibre bundling or entanglements,to achieve controlled feeding directly into port holes or orifices ofplastics processing machinery. Although some fibre—feeders exist theyare either expensive and/or unreliable or inaccurate in meteringuniformly over a wide range of fibre feed ratios with wood and othernatural fibres. In addition, it is necessary to pre-dry a highvolume-low mass of fibre before such feeding/use since such fibres arehygroscopic and retain, or reabsorb, high levels of water, which isusually undesired and required to be substantially removed prior to theplastic processing. (See, for a review of fibre feeders, John Winski,“Feeding Solutions for Wood Plastics Applications”, The 6thInternational Conference on Woodfiber—Plastic Composites, p 137-148).Thus, the processing and handling issues mentioned above associated withwood flour are much worse when one wishes to consider use of wood fibre.Hence, if a convenient and low cost method for the manufacture of woodfibre pellets existed this would be a breakthrough for wood fibreutilisation in plastics. Such products with suitable performance and/orconvenient, cost-effective, methods for their manufacture, are not wellknown or established. Feeding or metered additions of pellets intoextruders etc is much more convenient.

Medium density fibreboard (MDF) uses a high temperature thermomechanicalpulp fibre to produce large panels for a variety of applications, suchas furniture or internal mouldings. Due to the commercial scale of theseoperations and the use of heat to soften the fibres, MDF fibre is a lowcost form of wood fibre. Additionally, it has an aspect ratio to allowreinforcing of composites (for example radiata pine approx 2.5 mm×30μm). In the MDF process a thermosetting resin, typicallyurea-formaldehyde (UF) or related formaldehyde crosslinking resins, orother resins such as isocyanate resins, is added to the fibre, with thefibre in a wet state, while it is exiting the refiner in the blowline.This gives extremely high surface coverage of the fibre at low resinloadings⁽⁶⁾. The MDF process would not be usually associated withproducing a thermoplastic precursor for further processing in extrusionor other thermoplastic operations. Ordinarily it produces a sheetproduct which is fibre-rich and bound with a rigid, cured, thermosetresin which is not readily thermoplastically processable orreprocessable or easily usable or useful in thermoplastic processes.

Plastic and wood, or plastic and natural fibres, do not mix easily,although some polymers are more compatible than others are. PVC, whichis polar like wood, reportedly bonds to, or interacts well with, thefiller or fibre without special alloying or coupling agents, whereaspolyolefins (polypropylene and polyethylene) do not adhere to wood aswell as PVC, and so such wood-plastics require modification to get thebest level of performance from the filler or fibre in the plastic. Oneexample of the current state of technology is to add a coupling agent,often a maleated polyolefin for polyolefin based composites, into theextruder and mixing within the extruder. The prior art contains numeroussuggestions regarding polymer fibre composites. Gaylord, U.S. Pat. Nos.3,765,934, 3,869,432, 3,894,975, 3,900,685, 3,958,069 and Casper et al.,U.S. Pat. No. 4,051,214 teach a bulk polymerization that occurs in situbetween styrene and maleic anhydride monomer combined with wood fibre toprepare a polymer fibre composite. Segaud, U.S. Pat. No. 4,528,303teaches a composite composition containing a polymer, a reinforcingmineral filler and a coupling agent that increases the compatibilitybetween the filler and the polymer. The prior art also recognizesmodifying the fibre component of a composite. Hamed, U.S. Pat. No.3,943,079 teaches subjecting unregenerated discontinuous cellulose fibreto a shearing force in shear mixers, resulting in mixing of a polymerand a lubricant material with the fibre. Such processing improves fibreseparation and prevents agglomeration. Similarly, Coran et al., U.S.Pat. No. 4,414,267 teaches a treatment of fibre with an aqueousdispersion of a vinyl chloride polymer and a plasticizer, the resultingfibres contain a coating of polyvinyl chloride and plasticizer and canbe incorporated into the polymer matrix with reduced mixing energy.Beshay, U.S. Pat. Nos. 4,717,742 and 4,820,749 teach a compositematerial containing a cellulose having grafted silane groups. Raj etal., U.S. Pat. No. 5,120,776 teach cellulosic fibres pre-treated withmaleic or phthalic anhydride to improve the bonding and dispersibilityof the fibre in the polymer matrix. Raj et al. teach a high densitypolyethylene chemical treated pulp composite. Hon, U.S. Pat. No.5,288,772 discloses fibre reinforced thermoplastic made with a moisturepre-treated cellulosic material such as discarded newspapers having alignant content. Kokta et al., “Composites of Poly(Vinyl Chloride) andWood Fibres. Part II. Effect of Chemical Treatment”, Polymer Composites,April 1990, Volume 11, No. 2, teach a variety of cellulose treatments.The treatments include latex coating, grafting with vinyl monomers,grafting with acids or anhydrides, grafting with coupling agents such asmaleic anhydride, abietic acid (See also Kokta, U.K. Application No.2,192,397). Beshay, U.S. Pat. No. 5,153,241 teaches composite materialsincluding a modified cellulose. The cellulose is modified with an organotitanium coupling agent which reacts with and reinforces the polymerphase. Maldas and Kokta, “Surface modification of wood fibres usingmaleic anhydride and isocyanate as coating components and theirperformance in polystyrene composites”, Journal Adhesion ScienceTechnology, 1991, pp. 1-14 show polystyrene flour composites containinga maleic anhydride modified wood flour. A number of publicationsincluding Kokta et al., “Composites of Polyvinyl Chloride-Wood Fibres.III: Effect of Silane as Coupling Agent”, Journal of Vinyl Technology,Vol. 12, No. 3, September 1990, pp. 142-153 disclose modified polymer(other references disclosed modified fibre) in highly plasticizedthermoplastic composites. Additionally, Chahyadi et al., “WoodFlour/Polypropylene Composites: Influence of Maleated Polypropylene andProcess and Composition Variables on Mechanical Properties”,International Journal Polymeric Materials, Volume 15, 1991, pp. 2144discuss polypropylene composites having polymer backbone modified withmaleic anhydride.

Although many publications refer to wood fibres, in reality they areessentially wood flour or powders, or flakes, or saw-dust etc ratherthan fibres with a reasonable aspect ratio (10:1 or 20:1 or more, etc asdescribed above), for example typically of average length 1 mm or more.Flour and related materials are easier to handle and process and feedinto typical plastics machinery, whereas the longer fibres tend to beentangled and fluffed and much more difficult to feed into plasticsmachinery in a metered way.

Accordingly, a substantial need exists for improved processes tointroduce wood or other natural fibres, for example with an aspect ratiogreater than 10:1 or 20:1 or with an average fibre length of, say, 0.8mm or 0.9 mm or 1 mm or more (as opposed to wood flour or powders orflakes) into plastics processing machinery, and, also, forcompatibilising formulations or materials for combining thermoplasticpolymer(s) and wood or natural fibre(s).

In other prior art, Sears et al (9) describes use of fibres with analpha cellulose content purity >80% indicative of pulps which areusually kraft or chemically pulped and not ordinarily available ormanufactured by an MDF type process ie via mechanical orthermomechanical pulping methods such as used in the present invention.Fibre pellets with wet pulp cellulosic fibres can be manufactured inother ways such as use of granluated pulps impregnated with binders,which will often reduce fibre lengths and aspect ratios and result in aproduct which is similar to the use of wood flour, or via use of mixersin which fibres and aqueous, dissolved, binders are premixed (eg inHobart or similar mixer) in a water medium, and then pellitised wet, viaspecial pellet mills (eg Kahl Pellet Mill). Such methods are describedby Sears et al (9). These approaches will not be as convenient as thepresent invention in that significant drying and densification of thewet impregnated pulps is required prior to eventual introduction toplastics and the process or products are unlikely to be ascost-effective as an MDF manufacturing approach, and the fibre productsproduced therein. In addition, the use of blowline or related processeswhich use moving air or steam carried fibre streams and polymersolutions or dispersions applied therein, coat the fibres with a well orhighly dispersed polymer coverage on the fibre surface in highlyefficient manner with efficient usage of polymer. Furthermore the use ofthe MDF and related processes are well suited to low cost continuousmanufacturing processes.

OBJECT OF THE INVENTION

It is an object of the invention to provide an improved, or at least analternative process or method to introduce wood fibre or otherlignocellulosic or natural fibre, into plastics and for subsequentutilisation in plastics processing machinery.

SUMMARY OF THE INVENTION

In broad terms in one aspect the invention comprises a process forproducing pellets or granules (as herein defined) comprising fibres of alignocellulosic material or natural fibres, for use as a feedstock inplastics manufacture, which comprises:

conveying loose or divided fibres or fibre bundles, produced bymechanically or thermomechanically or chemo-thermomechanically orchemo-mechanically breaking down a lignocellulosic material, or naturalfibres, in a dry or wet air stream and applying to the fibreswhile so conveying the fibres a liquid formulation comprising one ormore polymers, monomers, or oligomers,forming the fibres into a solid product, andbreaking down the solid product to produce said pellets or granules.

Preferably the process includes conveying the fibres along a conduit ina dry

or wet stream and introducing the formulation of the polymer, mononmeror oligiomer into the interior of the conduit to apply the formulationto the fibres while the fibres are moving through the conduit.

Preferably the process includes introducing the formulation into theconduit by spraying the formulation into the interior of the conduit asthe fibres move through the conduit, to coat or partially coat thefibres.

Preferably the conduit conveys the fibres from a refiner stage in aplant for manufacture of fibre board.

Preferably the conduit conveys the fibres to or from a drying stage ordrier.

Preferably the process includes forming the fibres into a solid productby pressing the fibres to a solid product in planar form.

Preferably the process includes pressing the fibres between heatedplattens.

Preferably the process includes pressing the fibres into a sheet of upto about 2 cm in thickness, more preferable up to about 1 cm inthickness.

Preferably the process includes breaking down said solid product to saidpellets or granules by cutting or sawing the solid product.

Preferably the fibres have an average fibre length or fibre-bundlelength of at least about 0.8 mm, more preferably at least about 1 mm.

Preferably a major fraction of the fibres have an aspect ratio of atleast 10:1, more preferably at least 20:1, and most preferably at least25:1.

Preferably the process includes breaking down the solid product toproduce pellets which are longer than the average fibre length of thefibres within the pellets.

Preferably the pellets or granules comprise between 0.3 to 25 parts ofthe polymer per 100 parts of fibre by dried weights.

Preferably the liquid formulation is an aqueous solution, dispersion oremulsion.

Preferably the formulation comprise(s) a thermoplastic polymer having amelting point below 230° C., or below 200° C.

Preferably the polymer is a polyvinyl alcohol, polyvinyl acetate,polyester, starch based, or a polymer or copolymer with one or more ofan acid, anhydride, epoxy, amine, isocyanate, silane, or silanol group.

In a further aspect the invention comprises a process for producingpellets or granules (as herein defined) comprising fibres of alignocellulosic material or natural fibres, for use as a feedstock inplastics manufacture, which comprises:

conveying loose or divided fibres or fibre bundles, produced bymechanically or thermomechanically or chemo-thermomechanically orchemo-mechanically breaking down a lignocellulosic material, or naturalfibres, along a conduit in a dry or wet air stream,applying to the fibres a liquid formulation comprising one or morepolymers, monomers, or oligomers, by spraying the formulation onto thefibres to coat or partially coat the fibres,forming the fibres into a solid product, andbreaking down the solid product to produce said pellets or granules.

In a further aspect the invention comprises process for producingpellets or granules (as herein defined) comprising wood fibres, for useas a feedstock in plastics manufacture, which comprises applying to woodfibres or fibre bundles, produced by mechanically or thermomechanicallyor chemo-thermomechanically or chemo-mechanically breaking down solidwood, a liquid formulation comprising one or more polymers, monomers, oroligomers to coat or partially coat the fibres, pressing the fibres intoa solid product, and breaking down the solid product into woodfibre-containing pellets or granules.

The terms pellets or granules is intended to exclude powders and includelarger particles, comprising whole fibres, that are free flowing.

The term ‘comprising’ as used in this specification and claims means‘consisting at least in part of’, that is to say when interruptingindependent claims including that term, the features prefaced by thatterm in each claim will need to be present but other features can alsobe present.

Typically the invention provides a process of impregnating or coating orbinding wood and other natural fibres, such as cellulose based fibres,with a dispersed or dissolved polymer system (‘binder’), then pressingor consolidating the impregnated fibres under pressure, and preferablyat elevated temperature, into sheet or mat wherein the fibres are heldtogether largely by the binder and then chopping the sheets intofeedstock pellets or fibre concentrates.

In general the invention relates to a process or method for themanufacture of pre-coated or impregnated wood or other natural fibrecomposite feedstocks, such as pellets, or masterbatch compounds, usefulin thermoplastic processes. In particular, the invention describes amethod for producing wood or other natural fibre compounds or pellets,using fibres such as obtained from a thermo-mechanical pulping process,during, or after, which the fibres are treated with a coating or bindersystem, applied via a solution or dispersion or powder dispersion to aflowing or moving fibre stream, in air or steam, such as in a blowline.Such coating or binder holds the fibres together when formed or pressedor heated into a profile or sheet or other shape, and when suchpressings or shapes are chopped or comminuted into, for example,pellets, and the binder or coating which will also still allowsubsequent convenient feeding into, and processing in, plastic processesand machinery and mixing or moulding with other plastic materials. Theprocess may also include pre-coating or partially pre-coating orpre-compatibilising wood or other natural fibres, or introducing otherfunctional materials on, in, or close to, such fibres, which can then beprocessed into a convenient pellet or feedstock for use in plasticprocessing, and blending with plastics and other materials, especiallyin thermoplastic processes such as extrusion or injection moulding.

The invention provides a method for producing wood fibre pellets in asuitable form for feeding into thermoplastic processing equipment, suchas extruders or injection moulders. Preferably thermomechanical orthermo-mechanically refined pulp or chemo-mechanical pulp, orchemo-thermomechanical pulp, wherein optional pre-digestion of fibres orchips can occur before entering the fibre refiner, is used as the fibre.More preferably high temperature thermomechanical pulp, such as mediumdensity fibreboard fibre (MDF) is used. Thus, one embodiment of thisinvention uses modified MDF (medium density fibre board) processes toovercome the difficulties and issues highlighted above in fibre-feeding,fibre-drying and fibre-plastic compatibility.

In one embodiment, the fibre has a binder added in the blowline or otherfacility for spraying or distributing polymer dispersions or solutionsonto fibres. Preferably, the binder is a thermoplastic polymer, orcomprises a thermoplastic polymer as one component However, thermoset ormixed polymer systems are also possible. Preferably, the binder is inaqueous solution or an emulsified or aqueous polymer dispersion or aformulation of ingredients which is a dispersion, emulsion or solutionor a neat liquid. Any polymer which can be dissolved or dispersed inwater, or modified or formulated to form or be part of a stabledispersion, or polymerisable resin system, in water may be used.Alternative solutes or dispersion media may be used such as alcohols orother organic solvents, but water is the preferred medium, either aloneor in admixture with other co-solvents. Latexes may be used. Dry or neatpolymer powders may also be used under varying conditions and lowmelting waxes or polymers or blends, as high or 100% solids, may also beused according to viscosity and tack requirements of the applicationapparatus such as spray gun/nozzle. Heated tubing and heated nozzles maybe used to aid introduction of such materials.

The polymer or additives can be added in the refiner or in the bowlineor in the drier or at any point, prior to or after any of these stagesin the tubes or pipes or drums or other vessels which convey or transferfibre continuously in the process. The polymer/additives may be appliedto wet fibres or dried fibres or to fibres with equilibrium or nearequilibrium moisture content (EMC, typically of the order of 12 wt %moisture). The polymer coating is added to the flowing fibre, stream,which may contain bundles or fines, and which are entrained in air orhigh humidity air, at any point of the MDF process, or relatedfibre-refining—impregnation manufacturing processes.

Preferred polymers for the binder are polymers which can be processed asa thermoplastic substance or elastomers and are herein classified asthermoplastic substances and constitute a preferred subclass of plasticpolymers. Additionally thermoset resin may be used as binder. Examplesof elastomers suitable for the preparation of concentrates of thisinvention are natural rubber, styrene-butadiene rubber (SBR),ethylenepropylene rubber (EPR), ethylene-propylene terpolymer (EPDM),acrylonitrile butadiene rubber (NBR), ethylene-vinylacetate copolymer,silicone rubber, polybutadiene rubber, cis-polybutadiene,trans-polybutadiene, neoprene, polyisoprene and butyl rubber,sulfur-vulcanizable diene rubbers. Diene rubber includes rubber of bothlow and high unsaturation, the unsaturation being either in a side chainor in the backbone of the polymer and either conjugated ornon-conjugated. Examples of other suitable polymers include acrylatepolymers, urethane polymers, chlorosulfonated polyethylene, polyvinylchloride, halogenated polyethylene, polystyrene, polyvinyl acetate,polyvinyl alcohol, polyvinyl pyrrolidone, acrylonitrilebutadiene-styrene terpolymers (ABS), styrene-maleic anhydride copolymersand esterified or other derivatives, polyamides, polyesters, orcopolymers of vinyl acetate, copolymers of olefins (ethylene, propylene)with unsaturated acids such as acrylic or methacrylic acid or maleicanhydride or with vinyl alcohol or vinyl esters, polyvinyl ethers andcopolymers of vinyl ethers, starches and starch derivatives,polycaprolactone, polylactic acid, polyhydroxyalkanioates, proteins,polyacids, polyanhydrides, polyisocyanates, polyols/polyethers, andcopolymers or terpolymers and the like, containing the monomers of suchpolymers. Mixtures comprising one or more of the above are alsosuitable. Other oligomeric or reactive resin systems such as epoxyresins, acrylics, unsaturated polyesters, urethane/isocyanate resins,formaldehyde cure resins such as urea-formaldehydes,melamine-formaldehyde, phenol-resorcinol resins, phenolic resins, andrelated or hybrid systems may also be used. In the process of theinvention, resins such as those above or others may be formulated andused as the polymer and/or additives. Thus the added polymer(s) oradditives may include reactive monomers or oligomers with reactivegroups, applied as aqueous dispersions, emulsions or as neat liquids ormolten media.

In a preferred embodiment the binder may also act as a compatibiliserfor the fibre and bulk matrix plastic in the end composite, and, thus,the present invention allows a compatibiliser to be added to the fibreand binder in the blowline to afford greater bonding between polymersand wood fibre. The compatibiliser can be any of the polymers above ortheir mixtures or blends and can be, or contain, other added materialsalso. It may be a formulated or reactive polymer system. For polyolefinmatrix end composites it is preferably a maleated or acid functionalcopolymer, such as maleated polyproplyene. Preferably the compatibiliseris an emulsified or dispersed polymer or one dissolved in water.

Although in principle any fibre or filler can be used in the inventionthe advantages are most evident with fibres or other fillers which aredifficult to feed into plastics processing, or other, machinery in theirindividual, separated, loose, normal or other readily available forms.In particular cellulosic or ligno-cellulosic fibres are preferredespecially from natural origins such as wood (all types), plant or cropfibres (hemp, straw, wheat, flax, NZ flax, corn, coconut, grasses,kenaf, jute, sisal, ramie, kudzu, . . . ) and animal fibres such aswool/keratin, other protein fibres. Often such fibres have low bulkdensities and are entangled or curled fibre bundles difficult to flow orfeed into small orifices and to convey in metered way into extrudersetc.

Thus the present invention provides a solid panel, sheet or profile bycompacting, for example with heat and pressure in a press, the fibrewetted with added polymer. Preferably a hot press is used to compressthe fibre into a solid panel or sheet. The panel can then be comminutedinto pellets producing pre-compatibilised fibre concentrates which canthen be readily fed and metered into extruders or other plasticsprocessing machinery, usually with pre-drying. In one example of theinvention pellets containing wood fibre and polymer(s) can be preparedfor example by cutting or slicing the consolidated form resulting frompressing.

Although the present invention is broadly as defined above, thosepersons skilled in the art will appreciate that the invention is notlimited to it and that the invention also includes embodiments of whichthe following description gives examples.

The present invention is broadly directed to wood plastic composites(WPCs) and other natural fibre plastic composites, and preparation ofraw materials for eventual use in processing equipment such as plasticextruders or injection moulders and related equipment.

Accordingly, in one aspect, the invention provides a method of producingand compressing wood or natural or plant fibre into a form suitable forintroduction into plastics processing equipment, such as an extruder.The invention uses a press, for example a traditional MDF process orother refining process, to produce wood fibre from wood or natural plantfibre from plants, and then apply additives in the blowline or refinerand related processes. The fibre-additive blend is dried and formed intoa mat before pressing in a tradition MDF press to produce sheets. Thesheets are subsequently reduced to concentrates, agglomerates,particles, tapes or pellets that can be fed into plastics processingequipment. For example the sheets can be slit and pelletised with pelletlengths of any desired length according to the chopping length set andthe initial pressed sheet dimensions. Preferably the pellet length willbe longer than fibre length. For example 2 mm, 3mm or 4mm or 5 mm or 6mm or longer may be used.

To allow the MDF fibre to remain consolidated after pressing, a binderis added, for example into the blowline, shortly after fibres are formedin the process. Alternatively the fibres may be collected from therefining process and subsequently turbulently reflowed in a stream, thensprayed or impregnated with binder polymer solution or dispersion. Thebinder needs to have sufficient strength to hold the fibres in a sheetand in a solid pellet, when pelletised. Preferably, though notessentially, the binder should have a glass transition, melt,dissociation, softening or degradation temperature such that fibres areallowed to become mobile in the plastics processing equipment, such asin the barrel of an extruder, and form a uniform blend with thethermoplastic material it is being blended with. The binding polymer canbe added at low loadings solids on fibre, and not cause compatibilityproblems with the final polymer it is to be combined with.Preferentially the binder will act to improve compatibility between thefibre and bulk plastic matrix. Thus, a further aspect to the inventionis the addition of compatibilisers in the blowline, designed to improvethe compatibility and binding between wood or other fibres and thethermoplastic matrix the fibre will eventually be blended with. Blendingpolymers with fibres in a MDF blowline gives better surface coverage offibres than blending dry fibres with polymer at ambient conditions. Asthe blowline operates at elevated temperatures and moisture contents, itis preferable that the compatibiliser is in the form of an emulsion ordispersion in water. Neat liquids or low melting solids eg waxes mayalso be used if able to be sprayed into fine particles. Preferentiallythe binder coated fibres are pressed under heat to form a sheet withsufficient integrity to withstand slitting and pelletisation processes.This may also impart or retain intimate mixing, contact or bonding ofthe binder/compatibiliser with fibre and/or remove some of the moisture.

The process may typically be performed in many conventional MDF orparticleboard mills wherein fibres are refined and impregnated inblowline or similar facilities, pressed under heat, but, in the processof the invention, then slitted and chopped into pellets and,preferentially, the binder resin is a resin system which is compatiblewith the ultimate thermoplastic matrix of choice and processable inplastics machinery such as extrusion or injection moulding. Thus, it isfeasible that conventional MDF or similar mills, or their products,could be adapted to produce fibre concentrates for plastics extrusion orinjection moulding or other moulding processes, to make fibre-plasticcomposites. The binder or fibre pre-coating composition may be aformulation of one or more polymers and may also comprise otheradditives such as stabilisers, plasticisers, process aids, flameretardants, adhesion promoters, colourants, lubricants, anti-staticagents, bioactives, liquid additives or solids difficult to introduceinto the extruder or required at low levels overall and may also includereactive or functional resins such as epoxy resins.

The pressing of the intermediate sheets can be carried out according toa range of sheet densities. The pelletisation of such sheets can becarried out by a variety of methods and a range of pellet lengths anddimensions and shapes can be used. Pre-patterning or imprinting of thesheets can be carried during or after sheet manufacture out to aid thesubsequent pellet manufacture.

When mixing the fibre-rich pellets with plastic pellets and/or otheradditives in an extruder various combinations of mixing approaches andrelative positions of introduction are feasible.

The fibre pellet may be added directly to an injection moulding machine,with added plastic pellets.

The examples below illustrate the invention, though they are not to beconsidered in any way limiting and modifications can be made withrespect to the invention by one of ordinary skill in the art.

EXAMPLE 1 PVA Bonded MDF Fibre Pellets and Reference (Wood Flour)Pellets

Polypropylene (PP) was extruded with radiata pine MDF fibres and theninjection moulded to form test specimens. Wood flour and sander dust areused as references, as examples of wood derived fillers conventionallyused in industry and reasonably easy to feed in as particulate productscompared to a fibre product. Their performance levels, in the composite,are representative of industry or existing norms for compounded ormoulded wood reinforced plastics and is included here to demonstratethat performance is not compromised by the utilisation of the fibrematerials and processes of the invention. Fibre products are expected tobe at least equal to the flour products and superior to them in someproperties, as reinforcement, though, direct utilisation of loose lowdensity or entangled fibres is difficult in the feeding into extrudersand other machinery in a controlled or measured way. Tensile, flexuraland resistance to impact properties of the MDF fibre-reinforcedcomposite materials were determined as a function of fibre content andprocessing parameters and compared with flour products to ensureproperties are not compromised by using the methods of the invention tointroduce fibres rather than flour.

Materials

The MDF fibre used was produced at the New Zealand Forest Research PAPROpilot plant refiner from Pinus Radiata toplog using processingconditions to mimic commercial MDF fibre. The fibre was air dried toapproximately 10-15% moisture content before storage in plastic bags.Sander dust (SD) was supplied from local saw-mills. The PVA (polyvinylacetate) resin used was National Starch & Chemical (NZ) Limited Korlok442.3060.05. The polypropylene pellets used were Hyundai Seetec gradeM1600 with a melt index of 25.

Sample Production

PVA bonded MDF 2 mm panels were produced by spraying 80-100 grams of PVAresin onto 550 grams of fibre using the 500F MDF laboratory blender(Maxiblender), which uses air pressure to reproduce air turbulence, asin a blowline and blows fibres around or along a certain path, withresin application occurring via a nozzle or spray gun, forcing resininto the flowing fibre stream. 100 grams resinated fibre was then formedinto a 255 mm×280 mm×2 mm (700 kg/m³) panel or sheet, akin to MDFmanufacturing. The PVA bonded panels were cut into pieces approximately5 mm square, and such concentrates or pellets were desiccant dried undervacuum. The wood flour was dried at 80° C. for 24 hours. Thepolypropylene pellets were used as received without further drying. ThePVA bonded wood fibre and polypropylene pellets were mixed in an OMC19/30 twin screw co-rotating extruder: (19 mm screw, L:D 30).

The PVA/MDF fibre pellets were fed using a hopper and the polypropylenewas fed using a screw feed with extruder zone temperatures set asindicated in Table 1, though the pellets could be fed via a conventionalfeeder also.

TABLE 1 Extrusion conditions screw Zone 4 Zone 3 Zone 2 Zone 1 speedSample (° C.) (° C.) (° C.) (° C.) (rpm) all 180 180 170 160 200

The fibre pellets may be combined with plastics and other additives innumerous ways, according to common extrusion compounding practices andusing metered feeders etc.

Examples of variations demonstrated in this set of examples whichillustrate some options, but without limiting use of other approaches,were:

PM=fibre-pellets/PP pellets pre-mixed or introduced at the same port onthe extruderD=dual feed, fibre pellets in first port/PP pellets in second portF=dual feed, PP fibres in first port/fibre pellets in second portSD=wood flour (sander dust)/PP pellets pre-mixed or introduced at thesame port on the extruder (reference).

The wood flour was compounded by pre-mixing with polypropylene beforeintroduction into the first extruder feed throat using a U-shapedhopper.

The mixtures were extruded through a die, which formed a 3 mm-diameterstrand which was then pelletised. When problems occurred cutting thePP/wood flour strand during pelletising, the wood fibre/flourpolypropylene mixtures were Wiley milled through a 4mm mesh. The sameapproach was also used for the wood-fibre pellets for comparisons. Thefollowing wood fibre (PM, D, F) and wood flour (sanderdust—SD)/polypropylene mixtures were compounded as examples:

PM with 20% and 40% wood fibre (by weight)D with 20%, 40% and 60% wood fibreF with 25%, 30%, 40% and 60% wood fibreSD with 20%, 40% and 60% sander dust/wood flour (reference)

The compounded “pellets” were re-dried at 60° C. for 2-3 days beforeinjection moulding. The dry pellets were injection moulded using a Boy15S injection moulder (28 mm screw, 20:1 L:D), using processingconditions with a screw speed of 150 rpm, barrel temperatures in therange 190-230C, and tool temperature set at ambient.

Mechanical Property Testing

Samples were conditioned at 23° C. and 50% RH for 2 weeks beforemeasurement and testing.

Tensile properties were evaluated according to ASTM D638-96 (Type I)⁽⁷⁾.The specimens were a dog bone shape, with the narrow test section havinga nominal width of 13 mm and nominal thickness of 3.2 mm. An Instronmodel 5567 test machine was used for testing, equipped with a 10 kN loadcell and 25 mm extensometer. The initial separation between grips was100mm, with a testing speed of 5 mm/min.

Flexural properties were evaluated according to ASTM D790-96a⁽⁸⁾, exceptthat the loading nose and supports had radii of 7.5 mm. The specimenswere a rectangular shape, with a nominal width of 13 mm and nominalthickness of 3.2 mm. An Instron model 5567 test machine was used fortesting, equipped with a 10 kN load cell. A span of 50 mm and speed of1.3 mm/min was used for flexural tests.

Impact properties were evaluated according to ASTM D256-93a (Test MethodB—Charpy). The specimens were a rectangular shape, with a nominal widthof 13 mm and nominal thickness of 3.2 mm A CEAST 6545/000 testinstrument with supports 95.3 mm apart was used for testing, using a 0.5J hammer.

Tensile Properties

The tensile test results are presented below in Table 2.

TABLE 2 Tensile test results Tensile Ultimate Strain at Stress at Strainat Fibre/ Modulus Stress Break Yield Yield Sample Filler (GPa) (MPa) (%)(MPa) (%) PP None 1.39 25.2 40.9 13.6 1.09 M-PVA- MDF 2.18 20.8 8.0712.7 0.68 20PM bonded M-PVA- MDF 2.50 21.1 4.57 13.4 0.63 40PM bondedM-PVA- MDF 2.97 20.9 4.76 12.3 0.49 20D bonded M-PVA- MDF 4.21 20.8 3.1613.3 0.36 40D bonded M-PVA- MDF 8.71 17.8 0.36 7.9 0.14 60D bondedM-PVA- MDF 2.46 21.5 4.25 13.7 0.66 25F bonded M-PVA- MDF 3.45 22.2 3.5212.5 0.46 30F bonded M-PVA- MDF 4.60 24.2 3.12 10.2 0.26 40F bonded 20SDSander 1.97 21.6 5.79 12.6 0.73 dust 40SD Sander 3.41 20.5 2.97 12.50.43 dust PM = premixed PP with 20% and 40% wood fibre (both at starthopper, first port) D = PP fed separately with 20%, 40% and 60% woodfibre (in first port, PP in second) F = PP fed separately with 25%, 30%,40% and 60% wood fibre (second port, PP in first port) SD with 20%, 40%and 60% sander dust (reference - fed premixed at start hopper/firstport)

All filled polypropylenes had a significantly higher modulus with fibreusually higher than the wood powder (SD) reference. Tensile strengthsfor all composites were all lower than neat PP (polypropylene) which isindicative of poor fibre-polymer compatibility. However, the mainadvantage here was to provide a convenient method to introduce low bulkdensity fibres into an extruder or moulding machine using conventionalfeeders or approaches rather than special fibre stuffers or feeders. Itis much easier to feed in pellets cut from pressed sheets rather thanthe loose fibres or highly fluffy fibre bundles. Indeed, the use ofpellet feedstocks are preferred to using powders and fine particles. Theexamples above showed that pressed bound fibres even with thermoset PVAadhesive can be used as a feedstock pellet for thermoplastic processessuch as extrusion or injection moulding and achieve performance equal orsuperior to the powder reference.

Flexural Properties

The flexural test results are presented below. The polypropylenecontrol, 20% pre-mix and 20% sander dust samples did not break beforethey reached 5% strain, which is the limit of the ASTM test method. Thestress values given are at 5% strain. Beyond this point these specimensstill showed an increasing load.

TABLE 3 Flexural test results Flexural Stress at Stain at Stress atStrain at Modulus Break Break Yield Yield Sample (GPa) (MPa) (%) (MPa)(%) PP 1.05 33.8* 5.00** 20.9 2.20 20PM 1.98 39.0* 5.00** 21.7 1.23 40PM2.37 39.1 3.86 19.4 1.05 20D 2.57 38.9 3.54 24.0 1.13 40D 4.04 39.8 1.5731.0 0.90 60D 5.28 38.1 0.92 32.4 0.67 25F 2.14 38.8 3.87 23.6 1.21 30F2.81 40.3 2.54 26.5 1.04 40F 3.75 44.3 1.92 29.7 0.87 60F 4.61 34.0 1.0628.8 0.81 20SD 1.95 41.2* 5.00** 23.3 1.41 40SD 3.14 40.8 2.39 28.4 1.0660SD 4.19 33.1 1.29 25.3 0.68 PP = neat polymer SD = sander dust. Allothers = PVA-MDF fibre pellets. *samples did not break before 5% strain,values given are for stress at 5% strain **samples did not break before5% strain

Most of the filled polypropylenes had higher flexural strengths than thepolypropylene control with the materials made from pellets cut frompressed PVA-fibre sheets showing better performance than wood flour orsander dust (SD) references.

Impact Properties

The Table below shows that the fibre, as introduced by the methods ofthe invention, demonstrates higher impact performance than the powdersamples (SD) at equivalent loadings.

TABLE 4 Impact test results Impact Strength Sample (J/m) PP 102.50 20PM42.08 40PM 43.23 20D 45.27 40D 45.69 60D 30.00 25F 40.46 30F 41.16 40F53.51 60F 31.86 20SD 42.46 40SD 40.34 60SD 26.22

EXAMPLE 2 Use of Coupling Agents and Binders in Pre-Pelletised MDF FeedStock

Polypropylene composites containing natural fibres/fillers were producedby compounding in a twin screw extruder and subsequently injectionmoulding samples. Fibre (MDF), and wood flour, along with threedifferent coupling agents (polyvinyl acetate, maleic anhydride modifiedpolypropylene emulsion and solid maleic anhydride modifiedpolypropylene) were used.

Materials

The MDF fibre used was produced at the New Zealand Forest ResearchInstitute PAPRO pilot plant refiner from Pinus radiata toplog usingprocessing conditions to mimic commercial MDF fibre. The fibre was airdried to approximately 10-15% moisture content before storage in plasticbags. The wood flour used was standard grade Pinus radiata supplied byKingsland Seeds.

The polypropylene resin used was Hyundai Sétec grade M1600 supplied aspellets. Zinc stearate powder was AR grade obtained from BDH. The maleicanhydride modified polypropylene (MAPP) emulsion used was Michem 43040supplied by Michelman Inc. The PVA resin used was National Starch &Chemical (NZ) Limited Korlok grade 442.3060.05. Epolene G3015 (EastmanChemical Co) was also used as a source of solid MAPP, added into theextruder.

Sample Production

PVA and MAPP (Michem emulsion) bonded MDF 2 mm panels were produced byspraying resin emulsions/dispersions onto 550 grams of fibre, in aflowing stream, using the 500F MDF Maxiblender to obtain a resin solidsloading of either 4% or 8%. 100 grams of resin coated fibre was formedinto a 255 mm×280 mm×2 mm (700 kg/m³) MDF panel. The MDF panel was cutinto pieces approximately 5 mm square. All of the natural fibres andfillers were dried at 60° C. for 48 hours before compounding except forthe PVA bonded MDF, which was desiccant dried using silica gel undervacuum.

An OMC 19/30 twin screw co-rotating extruder (19 mm screw, L:D 30) wasused for compounding with a screw speed of 150-200 rpm and a temperaturerange of 160-210° C. The natural fibres/fillers and polypropylenepellets were fed in two separate streams. The polypropylene was fedfirst, followed by the natural fibre/filler partway along the extruderbarrel. The mixture was extruded through a die, which formed a 3mm-diameter strand. To minimise moisture uptake, the extruded strand wasnot cooled in a water bath and pelletised as standard, but was aircooled and ground using a Wiley mill through a 4 mm mesh. The samplesproduced are given below.

TABLE 5 Wood fibre polypropylene composites produced Composition (%)Michem Label Fibre fibre PP Epolene 3015^(a) 43040^(b) PVA^(b) M-M MDF36.8 60 — 3.2 — bonded M-ME MDF 38.4 58.25 1.75 1.6 — bonded M-PVA MDF36.8 60 — — 3.2 bonded WF wood flour 40 60 — — — WF-E wood flour 40 56.53.5 — — PP-E PP control 96.5 3.5 — — PP PP control 100 — — — ^(a)appliedin extruder ^(b)applied by spraying into the flowing fibre stream,pressed and bonded as in a MDF sheet-making process then chopped intofibre concentrates for mixing in extruder with PP to make pellets forfinal injection moulding. WF = references/control also.

The sample sets are labelled with the fibre type first (M=MDF, WF-woodflour) followed by any additives after the hyphen (E=Epolene solid MAPP,M=Michem MAPP emulsion, PVA=poly(vinyl acetate)).

The compounded materials were re-dried at 60° C. for 48-72 hours beforeinjection moulding. The dry pellets were injection moulded using a Boy15S injection moulder (28 mm screw, 20:1 L:D), using a screw speed of100-200 rpm, and a temperature range of 200-230° C.

In all cases the feeding in of pellets or chopped sheet into theextruders was much more convenient than using loose fibres (or flour),which were difficult to introduce uniformly in any metered way, and alsoeasier than handling of wood flour or sander dust.

Mechanical Property Testing

The samples were evaluated as to their tensile, flexural, and impactproperties as described in Example 1.

Tensile Properties

The tensile test results are given below Table 6.

TABLE 6 Tensile test results Strength/ Strain at Label MPa break/% M-M32.98 1.56 M-ME 46.58 1.83 M-PVA 20.81 3.16 WF 21.11 2.97 WF-E 29.561.77 PP 25.16 40.94 PP-E 23.23 6.71

Composite samples prepared with the MDF fibre were examples of theinvention. The PVA bonded example illustrates that other resins can beused to aid fibre introduction via the fibre pellet process and goodmoduli data are obtained. In this PVA case the fibre-PP (matrix)interaction is unoptimised. The use of alternative, more polar, matrixand/or added coupling in the matrix would be able to be used to improvethe overall performance in using PVA, or other adhesively bonded MDF.The use of PVA and Michem adhesives to bind MDF into sheets prior topellet-making from the sheets, were applied via an example of theprocess of the invention to the MDF fibre composites led to increases inthe tensile modulus. SEM micrographs of the composites show thedifferent types of fibre are separated rather than being in fibrebundles, such as may be originally present in the fibre concentrates orpressed sheets.

The addition of natural fibre reduced the maximum tensile stress of theuncoupled polypropylene composites in all cases. There were nosignificant differences in the tensile strength of the different fibrecomposites when no additives were used.

The addition of Michem (via precoating, sheet-making and chopping intofibre concentrate prior to extrusion ad injection moulding) increasedthe maximum tensile stress above that of unfilled polypropylene. Theexamples M-M and M-ME represent examples of the invention in a preferredmode, wherein the binder is applied can also act as compatibiliser.Superior properties are observed.

Thus, the invention has provided a convenient route to introducingfibres and compatibiliser into plastics via the use of precoatedpellets, prepared by essentially an MDF-type process, followed bycutting of the MDF-like sheet.

Flexural Properties

The flexural test results are given in Table 7. The stress (strength)values given are at 5% strain. Beyond this point these specimens stillshowed an increasing load.

TABLE 7 Flexural test results Modulus/GPa Strength/MPa M-M 3.59 57.95 M-4.04 39.78 PVA WF 3.14 40.78 WF-E 3.06 53.55 PP 1.05 33.81 PP-E 1.0638.29 * samples did not break before 5% strain, values given are forstress at 5% strain

The addition of the natural fibres increased the flexural modulus of allsamples compared to unfilled polypropylene. The addition of Michem orPVA improved the flexural modulus of the MDF composites. The addition ofthe natural fibres increased the maximum flexural stress of all thecomposites compared to unfilled polypropylene. The addition of Michemalso improved the flexural strength.

Impact Properties

The impact strength test results for natural fibre filled polypropylenecomposites are listed below in Table 8.

TABLE 8 Impact test results Impact Energy J/m2 M-M 46.5 M-ME 45.5 M-PVA45.7 WF 40.3 WF-E 43.7 PP 102.6 PP-E 105.3

The MDF (M) fibre samples gave higher impact strengths than the woodflour (WF) samples.

Thus, in summary the use of longer aspect ratio fibres (eg MDF fibres)manufactured as pellets with compatibilser, manufactured and introducedvia the methods of the invention lead to superior performance instrength, stiffness and impact properties compared to wood Sour orsimilar products. Even uncompatiblised (for PP matrix; PVA bonded/coatedfibres) pellets have equivalent or superior performance touncompatibilised wood flour usage, and are more easily handled andprocessed in metered additions.

EXAMPLE 2A

In a further set of composites produced as described in Example 2, atdifferent fibre loadings (20-60 wt %) the following data were obtained,illustrating that the unoptimised fibre-pellets perform better than woodflour, in addition to being more readily introduced to plasticsprocessing machinery.

TABLE 9 Impact strength of Further Composites Impact Strength AverageSample (J/m) 20% M-PVA 45.27 40% M-PVA 45.69 60% M-PVA 30.00 20% WF42.46 40% WF 40.34 60% WF 26.22

Commonly used resins for MDF such as urea-formaldehyde (UF) resins,melamines, isocyanates etc as well as PVAs—and other common resins, mayalso be used with good effect to aid fibre pellet manufacture forsubsequent introduction in to extruders or injection moulders

EXAMPLE 3 Wood Fibre Biopolymer Composites Materials and SampleProduction

Three resins, a starch, a poly-vinyl alcohol (PVAl), and amelamine-urea-formaldehyde (MUF) resin were each, added, in separateexperiments, to MDF fibre (thermomechanical pulp from the MDF refinerblowline at NZ Forest Research Institute, Run 128), by spraying orinjecting the polymer additives, as a dispersion or solution in water,using a Laboratory Maxiblender. The Maxiblender blows a fibre streamwith air or steam or gas with high turbulence, and has an injection portfor spraying resin or additives onto the flowing fibre stream. Theimpregnated MDF fibres were then collected and pressed into twomillimetre thick 300×300 mm panel using heat and pressure andsubsequently processed into 5mm square pellets. The MDF pellet squareswere made from sheet and extrusion compounded with biopolymer PLA(polylactic acid) and polyhydroxybutyrate (Biopol) at 180-200° C.Various compositions of fibre reinforced biopolymers with 40% (w/w)fibre content were thus made and pelletised and then injection mouldedinto test specimens, as listed in Table 10 below.

TABLE 10 List of MDF filled-biopolymer composites made. Polymer Label BP= Biopol; PLA = polylactic acid Description of Fibre and Additives BP -4% Starch^(a)  40% MDF squares from Run 128 with 4% Gelose starch173/60% Biopol G400 BP - 4% PVAl^(a)  40% MDF squares from Run 128 with4% poly-vinyl-alcohol/60% Biopol G400 BP - 2% MUF^(a)  40% MDF squaresfrom Run 128 with 2% melamine-urea-formaldehyde/60% Biopol G400 Pure BPPolymer 100% Biopol G400 PLA - 4% Starch^(a)  40% MDF squares from Run128 with 4% Gelose starch 173/60% PLA 3001D PLA - 4% PVAl^(a)  40% MDFsquares from Run 128 with 4% poly-vinyl-alcohol/60% PLA 3001D Pure PLAPolymer 100% PLA 3010D ^(a)applied by spraying into the fibre stream

The additives used were a melamine-urea-formaldehyde (MUF) added at twopercent, an Aldrich 90% hydrolysed poly-vinyl alcohol (PVAl), and aPenford's plasticised Gelose starch 173.

The poly-vinyl alcohol (PVAl) was dissolved into solution at 10% solidsusing a temperature-controlled stirrer-hotplate to keep the temperatureat 90° C. The solution was then cooled and the solution sprayed onto thefibre. Due to the low solids the fibre had to dried for two hours beforebeing resprayed with a second quantity (2% based on solids to MDF fibresolids) to bring the level of additive up to the required, for thiscomparison, 4% solids. Lower or different levels may be applied. Theinvention provides a convenient route to introducing difficult materialssuch as polyvinylacohol (commonly available as solutions or films) in toreinforced plastics by first pre-coating the fibres and then pelletisingvia the MDF-type processes and pressing methods.

Penford's Gelose Starch 173 was dissolved in a mixture of water andglycerol (20:80) to prepare the plasticised starch for spraying onto MDFfibre (27.31% starch content in dispersion)/solution).

Reference samples with wood flour added at 40 wt % in biopolymer werealso produced (PLA-WF and BP-WF). The wood flour¹ (WF) used was standardgrade Pinus radiata supplied by Kingsland Seeds. A sieve analysis of theflour indicated a particle distribution with >77%<250 microns.

Size Weight (mm) (g) % <0.063 0.04 0.2 0.063-0.125 0.36 27.3 0.25-0.5 0.75 49.8 0.5-1   2.5 15 >1 1.37 7.2 0.01 0.8

The bioplastics were dried according to manufacturer's recommendations,typically from 60-80° C. for 2-4 hours.

An OMC 19/30 twin screw co-rotating extruder (19 mm screw, L:D 30) wasused for compounding with a screw speed of 120 rpm and a temperaturerange of 140-170° C. for Biopol extrusion and 170-190° C. for PLA. Theprecompressed MDF squares and biopolymer pellets were fed in twoseparate streams. The biopolymer was fed first, followed by the MDFsquares partway along the extruder barrel, nearer the exit die. The 40%MDF/60% biopolymer and additives were extruded through a die, whichformed a 3 mm-diameter strand. The strand was pellitised with aLaboratory Pelletiser.

The Biopol-MDF compounded materials were re-dried at 60° C. for 24 hoursbefore injection moulding into test specimens. The test specimens weremoulded using a Boy 15S injection moulder (28 mm screw, 20:1 L:D), usinga screw speed of 100-200 rpm, and a screw temperature range of 150-190°C.

PLA-MDF compounded materials were re-dried at a temperature of 80° C.for 24 hours before injection moulding into test specimens. The testspecimens were moulded using a Boy 15S injection moulder (28 mm screw,20:1 L:D), using a screw speed of 100-200 rpm, and a screw temperaturerange of 165-210° C.

The compounded WF pellets were re-dried at 40° C. until the moisturecontent was below 0.5%, typically for 5-8 days, then dried at 80° C. fortwo hours immediately before injection moulding. The dry pellets wereinjection moulded using a Boy 15S injection moulder (28 mm screw, 20:1L:D) using similar conditions as above.

Mechanical Property Testing

Samples were conditioned at 23° C. and 50% RH for 1 week beforemeasurement and testing.

Flexural properties were evaluated according to ASTM method D790-96a⁽⁸⁾,except that the loading nose and supports had radii of 7.5 mm. AnInstron model 5567 test machine was used for testing the three pointbending specimens and was equipped with a 10 kN load cell. A span of 50mm and speed of 1.3 nm/min was used for flexural tests.

The densities and flexural properties of the MDF filled biopolymercomposites are given below in Tables 11 and 12.

TABLE 11 Densities of MDF filled Biopolymer samples Density Label ofAverage Sample (kg/m³) BP - Starch 1304 BP - PVAl 1296 BP - MUF 1293Pure BP polymer (neat) 1234 PLA - Starch 1310 PLA - PVAl 1303 Pure PLApolymer (neat) 1254

TABLE 12 Flexural Properties of MDF-Biopolymers Stress at Modulus MaxLoad Sample (GPa) (MPa) PLA - Starch 6.92 100.9 PLA - PVAl 7.93 110.6PLA - neat 3.82 116.6 PLA - WF ref 6.43 78.4 BP - Starch 4.58 54.8 BP -PVAl 6.43 61.0 BP - MUF 5.23 51.9 BP - neat 2.52 50.5 BP - WF ref 5.4545.5 Neat = plastic without fibre present. WF = wood flour added at 40%.Others = 40% loading fibre, as in Table 10 above-with pre-impregnatedMDF fibre, according to the invention.

Significant improvements in properties such as strength are achieved inthe bioplastics by use of the pre-coated fibre pellets as manufacturedby the process of the invention, compared to a wood flour reference.Particular benefits are seen from the use of polyvinylalcohol as thefibre coating. Modified polyvinyl alcohols and/or copolymers may beexpected to perform well as fibre coatings also. Even the use of MUF, athermoset resin binder, provides performance advantages over referencematerials (wood flour), in addition to aiding introduction of wood fibreinto the extruder or moulding machine.

EXAMPLE 4 Direct Injection Moulding of Pellets Made by the Invention

Wood fibre pellets with polyvinylacetate National Starch; 4% dry weightloading on fibres) were manufactured according to the invention aspreviously described and cut into 5 mm squares and dried. The pelletswere then injection moulded with added PLA, as above with simplepre-mixing of the fibre pellets with added plastic (PLA)_pellets toproduce injection moulded samples.

The directly injection moulded fibre pellets with added polymerexhibited a flexural strength of 67.9 MPa and a flexural modulus of6.27GPa at a fibre loading in the final plastic composite of about 20 wt%. Thus this high modulus was achieved with fibres present at a loadingof ˜20 wt %—about half that of the wood flour loading used in Example 3to achieve a similar modulus. Through simple optimisation of theadditives, as described earlier, further enhanced performance would beachieved. This demonstrates that direct injection moulding (nointermediate extrusion compounding) of the fibre pellets with addedpolymer can be achieved.

EXAMPLE 5 MDF Manufacturing Pilot Plant Trials

Trials at an MDF pilot plant at NZ Forest Research Institute wereundertaken using refiner-blowline polymer addition, as in the MDF orparticleboard industries, for the production of fibre-polymer pelletfeedstocks for use in plastic processes.

Fibre from wood chips was produced in the Forest Research MechanicalPulping Pilot Plant under typical conditions for hightemperature/mechanical pulps, as used in MDF industry.

Michem 43040 emulsion was added to hot fibre in the MDF refiner-blowlineand dried at 140° C. in a tube drier to a targeted moisture content of12 to 16%. The MDF fibre was pressed into two millimetre thick 300×300mm panels at three densities (500, 700 and 900 kg/m³) and subsequentlyprocessed (chopped) into 5 mm squares. The MDF squares were made fromsheet with coupling agent additives and then extrusion compounded withpolypropylene on an extruder at 180-200° C. Various compositions offibre reinforced polypropylene with 40% (w/w) fibre content were thenmade and pelletised before being injection moulded into test specimens.

The results indicate that the addition of an emulsified coupling agentor binder to the blowline of a commercial MDF plant and manufacturing ofthe pellets in a process representative of commercial MDF orparticleboard manufacturing, will give a similar performance to thelaboratory examples earlier and with a performance and processabilitysuperior to wood flour equivalents.

The binder or coupling agent may be added at various points in therefiner-blowline process and could be added at the refiner, or atvarious points along the blowline. Two or more points of addition may beused to apply the same or different polymers or additives sequentially.

Materials

Example trial fibres of thermo-mechanical pulp —MDF fibre were producedon the PAPRO pilot plant refiner at Forest Research, Rotorua. Fibre 129had 4% Michem emulsion injected onto the fibre which was flowing in theblowline.

The polypropylene resin used was Hyundai Séetec grade M1600 supplied aspellets. The maleic anhydride modified polypropylene emulsion used wasMichem 43040 (a non-ionic emulsion) supplied by Michelman Inc.

Approximately 20 kg of coated fibres for each run was dried using theMDF drying tube to blow hot (140-160° C.) air onto fibre that wascollected with a cyclone dropping the fibre into a plastic bag.

The fibre was measured for moisture content and adjustments made tocorrect for variation in moisture content. Michem 43040 was added to hotfibre at the MDF refiner blowline and coated fibre was dried at 140° C.to a targeted moisture content of 12 to 16%. The MDF fibres were pressedinto two millimetre thick 300×300 mm panels at three densities (500, 700and 900 kg/m³) at 180 C and subsequently processed or chopped into 5 mmsquares. The pellets were compounded with polypropylene on an extruderat 180-200° C. and pelletised before being injection moulded into testspecimens. Other dimensions for the sheets or the pellets are of courseentirely feasible. All of the pre-compressed MDF squares, with couplingagent, were dried at 60° C. for 48 hours before compounding.

The samples produced are listed below in Table 13.

TABLE 13 List of MDF fibre-plastics made. Density Description of 2 mmPanel Label of Fibre and Coupling Agents (kg/m³) 500M4 Run 129 4% Michemaddition 500 700M4 Run 129 4% Michem addition 700 900M4 Run 129 4%Michem addition 900 ^(b)applied by spraying onto fibre

-   -   500M4-900M4: MDF fibres as above, pressed in the presence of 4%        Michem G3015 coupling agent that was added in the blowline.        Fibre hot-pressed at 180° C. for 1 minute to different        densities.

An OMC 19/30 twin screw co-rotating extruder (19 mm screw, L:D 30) wasused for compounding with a screw speed of 180 rpm and a temperaturerange of 180-200° C. The pre-compressed MDF squares and polypropylenepellets were fed in two separate streams. The polypropylene was fedfirst, followed by the MDF squares partway along the extruder barrel.The 40% MDF (with coupling agents precoated/applied)/60% polypropyleneagents mixture was extruded through a die, which formed a 3 mm-diameterstrand which was pelletised into ˜5 mm length pellets using a laboratorypelletiser.

The compounded materials were re-dried at 60° C. for 24 hours beforeinjection moulding into test specimens. To ensure the test specimencompletely filled the mould cavity. The test specimens were mouldedusing a Boy 15S injection moulder (28 mm screw, 20:1 L:D), using a screwspeed of 100-200 rpm, and a temperature range of 200-245° C.

Mechanical Property Testing

Samples were conditioned at 23° C. and 50% RH for 1 week beforemeasurement and testing.

Tensile properties were evaluated according to ASTM method D638-96 (Type1)⁽³⁾. An Instron model 5567 test machine was used for testing, equippedwith a 10 kN load cell and 25 mm extensometer. The initial separationbetween grips was 100 mm, with a testing speed of 5 mm/min.

Flexural properties were evaluated according to ASTM method D790-96a⁽⁸⁾,loading nose and supports had radii of 7.5 mm. An Instron model 5567test machine was used for testing, equipped with a 10 kN load cell. Aspan of 50 mm and speed of 1.3mm/min was used for flexural tests.

Sample Densities

The densities of the MDF filled polypropylene composites are given belowin Table 14.

TABLE 14 Densities of MDF filled polypropylene samples Label Density FRRefiner/Blowline 500M4 1047 700M4 1054 900M4 1060 PP 890

Tensile Properties

The tensile test results are given below in Table 15.

TABLE 15 Tensile test results Strength/ Sample Modulus/GPa MPa Strain/%500M4 4.66 42.7 1.97 700M4 4.39 41.2 1.78 900M4 4.63 39.4 1.55 PP 1.3925.2 40.9

Flexural Properties

The flexural test results are given below in Table 16.

TABLE 16 Flexural test results Stress at Modulus Max Load 500 M4 4.3372.9 700 M4 4.37 71.8 900 M4 4.54 71.5 PP 1.05 33.8 * samples did notbreak before 5% strain, values given are for stress at 5% strain

The addition of Michem 43040 binder dramatically improved the tensileand flexural strength of MDF fibre/polypropylene. There was nosignificant gain in performance when the level of Michem 43040 wasincreased from 4%, though other levels including lower loadings areentirely feasible. The addition of Michem 43040 to MDF fibre in thepilot plant blowline indicates a similar level of performance achievedin the Laboratory Blender trials. MDF sheet at various densities wereable to be used as feedstock for pellets.

REFERENCES

-   1 Schut Jan. H., Wood is Good for Compounding, Sheet & Profile.    Online article from    http:/www.plasticstechnology.com/articles/99903fa1.html (1999).-   2 North Wood Plastics Inc., 3220 Crocker Avenue, Sheboygan, Wis.    53081 USA. http://www.northwoodplastics.com-   3 Brooke, J. G., Goforth, B. D., Goforth, C. L., U.S. Pat. No.    5,082,605, 1992.-   4 Deaner, M. J., Puppin, G., Heikkila., U.S. Pat. No. 5,827,607,    1998.-   5 Stark, N. M., Rowlands, E. R. (2003). Effects of wood fiber    characteristics on mechanical properties of wood/polyproplyene    composites. Wood and Fiber Science, 35(2), pp 167-174.-   6 Loxton, C., Thumm, A., Grigsby, W. J., Adams, T. and Ede, R.    (2000). Resin Distribution in Medium Density Fibreboard:    Quantification of UF Resin Distribution on Blowline Blended MDF    Fibre and Panels. In Proc. 5th Pacific Rim Biobased Composites    Symposium, Canberra, December 10-13, pp 234-242.-   7 ASTM D638-96: Standard Test Method for Tensile Properties of    Plastics.-   8 ASTM D790-96a: Standard Test Method for Flexural Properties of    Unreinforced and Reinforced Plastics and Electrical Insulating    Materials.-   9 Sears K. D et al (2001). Proc. 6^(th) International Conference on    Woodfibre Plastics Composites, Forest Products Society, 2001, p    27-34 and U.S. Pat. No. 6,270,883.

1: A process for producing pellets or granules (as herein defined)comprising fibres of a lignocellulousic material or natural fibres, foruse as a feedstock in plastics manufacture, which comprises: conveyingloose or divided fibres or fibre bundles, produced by mechanically orthermomechanically or chemo-thermomechanically or chemo-mechanicallybreaking down a lignocellulousic material, or natural fibres, in a dryor wet air stream and applying to the fibres while so conveying thefibres a liquid formulation comprising one or more polymers, monomers,or oligomers, forming the fibres into a solid product, and breaking downthe solid product to produce said pellets or granules. 2: The processaccording to claim 1 including conveying the fibres along a conduit in adry or wet stream and introducing the formulation of the polymer,mononmer or oligiomer into the interior of the conduit to apply theformulation to the fibres while the fibres are moving through theconduit. 3: The process according to claim 2 including introducing theformulation into the conduit by spraying the formulation into theinterior of the conduit as the fibres move through the conduit, to coator partially coat the fibres. 4: The process according to claim 3wherein the conduit conveys the fibres from a refiner stage in a plantfor manufacture of fibre board. 5: The process according to claim 4wherein the conduit conveys the fibres to or from a drying stage ordrier. 6: The process according to claim 1 including forming the fibresinto a solid product by pressing the fibres to a solid product in planarform. 7: The process according to claim 6 including pressing the fibresbetween heated plattens. 8: The process according to claim 6 includingpressing the fibres into a sheet of up to about 2 cm in thickness. 9:The process according to claim 6 including pressing the fibres into asheet of up to about 1 cm in thickness. 10: The process according toclaim 1 including breaking down said solid product to said pellets orgranules by cutting or sawing the solid product. 11: The processaccording to claim 1, wherein the fibres have an average fibre length orfibre-bundle length of at least about 0.8 mm. 12: The process accordingto claim 1, wherein the fibres have an average fibre length of loosefibres or of fibre bundles of at least about 1 mm. 13: The processaccording to claim 11, wherein a major fraction of the fibres have anaspect ratio of at least 10:1. 14: The process according to claim 11,wherein a major fraction of the fibres have an aspect ratio of at least20:1. 15: The process according to claim 11, wherein a major fraction ofthe fibres have an aspect ratio of at least 25:1. 16: The processaccording to claim 1, including breaking down the solid product toproduce pellets which are longer than the average fibre length of thefibres within the pellets. 17: The process according to claim 1 whereinthe fibres are wood fibres. 18: The process according to claim 1including breaking down the solid product down to produce pellets orgranules by chopping and including applying to the fibres sufficient ofthe polymer, monomer or oligomer formulation to bind the fibres togetherto withstand pelletisation or granulisation by chopping. 19: The processaccording to claim 1, wherein the pellets or granules comprise between0.3 to 25 parts of the polymer per 100 parts of fibre by dried weights.20: The process according to claim 1 wherein the liquid formulation isan aqueous solution, dispersion or emulsion. 21: The process accordingto claim 1 wherein the formulation comprise(s) a thermoplastic polymer.22: The process according to claim 21 wherein the thermoplastic polymerhas a melting point below 230° C. 23: The process according to claim 21wherein the thermoplastic polymer has a melting point below 200° C. 24:The process according to claim 23, wherein the polymer is a polyvinylalcohol, polyvinyl acetate, polyester, starch based, or a polymer orcopolymer with one or more of an acid, anhydride, epoxy, amine,isocyanate, silane, or silanol group. 25: The process according to claim24 including subsequently applying one or more second polymers,monomers, or oligomers or paraffin or wax to the fibres 26: The processaccording to claim 6 wherein said pressing step comprises first andsecond pressing operations, said second pressing operation being carriedout at a higher temperature than said first pressing operation. 27: Aprocess for producing pellets or granules (as herein defined) comprisingfibres of a lignocellulousic material or natural fibres, for use as afeedstock in plastics manufacture, which comprises: conveying loose ordivided fibres or fibre bundles, produced by mechanically orthermomechanically or chemo-thermomechanically or chemo-mechanicallybreaking down a lignocellulousic material, or natural fibres, along aconduit in a dry or wet air stream, applying to the fibres a liquidformulation comprising one or more polymers, monomers, or oligomers, byspraying the formulation onto the fibres to coat or partially coat thefibres, forming the fibres into a solid product, and breaking down thesolid product to produce said pellets or granules. 28: The processaccording to claim 27 wherein the conduit conveys the fibres from arefiner stage in a plant for manufacture of fibre board and includingforming the fibres into a solid product by pressing the fibres to asolid product in planar form. 29: A process for producing pellets orgranules (as herein defined) comprising wood fibres, for use as afeedstock in plastics manufacture, which comprises applying to woodfibres or fibre bundles, produced by mechanically or thermomechanicallyor chemo-thermomechanically or chemo-mechanically breaking down solidwood, a liquid formulation comprising one or more polymers, monomers, oroligomers to coat or partially coat the fibres, pressing the fibres intoa solid product, and breaking down the solid product into woodfibre-containing pellets or granules. 30: The pellets or granulesproduced by claim
 1. 31: The process for manufacture of plasticsproducts or intermediates which includes introducing pellets or granulesby the process of claim 1 as a feedstock into a plastics extrusion ormoulding machine.